1. Field of the Invention
The present invention relates to a laminated heat exchanger constituted by laminating tube elements and fins alternately over a plurality of levels, which is used, for instance, in the cooling cycle of an air conditioning system for vehicles.
2. Description of the Related Art
This type of laminated heat exchanger, which has been in development by this applicant, is constituted by laminating a plurality of tube elements alternately with fins. Each of these tube elements is provided with a pair of tanks at one end in the direction of the length and the tanks of the laminated tube elements constitute tank groups by communicating with one another as necessary through communicating holes formed in the direction of the lamination. In addition, the pair of tanks formed in each tube element communicate with each other through a U-shaped heat exchanging medium passage formed in the tube element. A communicating pipe for communicating between intake/outlet portions provided at one end of the laminated heat exchanger and one of the tank groups, is provided between a pair of tank groups that are parallel to the direction of the lamination and this communicating pipe allows heat exchanging medium to be induced into specific tanks. Note that each tube element is constituted by bonding two formed plates face-to-face.
The communicating pipe is mounted on the heat exchanger after the heat exchanger core is formed by laminating the tube elements and the fins, by fitting it into a grooved portion that is formed between the tank groups running parallel to the direction of the lamination and then by brazing it along with the heat exchanger core.
To elaborate on the above, as shown in FIG. 30, a tube element 200 is formed by bonding two formed plates 201 face-to-face, with each formed plate 201 having a brazing margin 203 and a flange 202 which is bent toward the unbonded side in order to improve the strength. In addition, each tube element 200 is provided with a pair of tanks 204 and 205 formed at one end, with a grooved portion 208 formed between the pair of tanks 204 and 205 so that the communicating pipe 206 is mounted in the grooved portion 208. This communicating pipe 206 is brazed while in contact with the flange 202 which is positioned around the grooved portion 208. Note that reference number 207 indicates the brazing material.
However, in a laminated heat exchanger that is structured as described above, since the flange 202 is bonded to the communicating pipe 206 as shown in FIG. 31, if a brazing defect occurs, a roughly triangular gap A may result between the flange 202 and the communicating pipe 206.
If water (condensation, water taken in through the intake port or the like) enters this gap A, as indicated with the arrow in FIG. 31, the water tends to be retained within the gap A, since it will not easily evaporate. This water is then likely to freeze and melt repeatedly due to temperature changes in the heat exchanger, which will cause the brazing margins in the tube elements to be damaged due to the expansion and contraction of the water through such freezing and melting. This will result in leakage of heat exchanging medium.
Moreover, there is a potential problem of the tube elements and the communicating pipe becoming corroded by the water retained in the gap A.